1. Field of the Invention
The present invention relates to a method for the preparation of graft polymer dispersions having a broad particle size distribution and a solids content of above about thirty percent by weight without wildly fluctuating viscosities. The present invention also relates to foams and molded articles formed by the graft polymer dispersions of the present invention.
2. Description of the Related Art
The related art as evidenced by U.S. Pat. Nos. 3,652,658; 3,875,258; 3,950,317; and Reissue Patent Nos. U.S. Pat. No. Re. 28,715 and U.S. Pat. No. Re. 29,014 discloses the preparation of graft polymer dispersions which are useful in the preparation of polyurethanes by the polymerization of ethylenically unsaturated monomers in polyols. U.S. Pat. No. 3,931,092 discloses the preparation of polymeric solids by carrying out the polymerization in the presence of a free radical initiator and an organic solvent.
Chaudhary, U.S. Pat. No. 4,012,462 discloses high impact polymers having broad particle size distribution. The polymers of Chaudhary are rubber polymers and the particle size distribution is achieved by a bulk suspension three-step polymerization process.
Swoboda et al, U.S. Pat. No. 4,224,419 disclose a mixture of styrene and acrylonitrile copolymers which are toughened with rubbery acrylic ester polymers. Products formed from this material have high impact weather resistant properties. The thermoplastic compositions of Swoboda et al are basically a mixture of a first graft copolymer, which is formed by a crosslinked acrylic ester polymer and a mixture of styrene and acrylonitrile, and a second separately prepared, graft copolymer which is formed from a crosslink of an acrylic ester polymer and a mixture of styrene and acrylonitrile. The two graft copolymers are then mixed with a hard component which consists of one or more copolymers of styrene and/or a-methyl styrene with acrylonitrile.
Hosoi et al, U.S. Pat. No. 4,624,987 disclose a vinyl chloride polymer composition containing 5 to 50 percent MBS resin which is prepared by first graft polymerizing a monomer component and a methacrylate onto a styrenebutadiene rubber and onto that copolymer, secondly graft polymerizing a vinyl monomer to obtain a substantially uniform particle size within the composition. The products formed therefrom have excellent solvent-resistance, transparency and impact-resistant properties.
Ramlow et al, U.S. Pat. No. 4,334,049 disclose a process for the preparation of finely-divided solid polymers in a polyol. These compositions are prepared by free radical polymerization on ethylenically unsaturated monomers in an organic solvent employing an alkylene oxide adduct of a styrene-allyl alcohol copolymer stabilizer.
None of the related art, insofar as is known, either alone or in combination, teaches the method of preparation of graft polymers of the present invention. None of the art, alone or in combination, would suggest to one of ordinary skill in the art that viscosity fluctuations in graft polyol samples may be eliminated or greatly reduced by the method of preparation as disclosed in the present invention. None of the references discloses the preparation of graft polyol dispersions using a continuous process to produce a seed graft polyol having up to 30 percent solid polymer dispersion, and, in a semi batch process, using the graft polyols prepared in the continuous process, as seeds to produce a graft polyol having 30 percent or more solids content and a relatively uniform viscosity from sample to sample.